Method for making an alkali metal salt of heptagluconic acid



Nov. 7, 1967.

METHOD FOR MAKING AN 'ALKALI METAL SALT OF HEPTAGLUCONIC ACID Original. Filed Oct. 12, 1961 7L CONVERSION VERSUS'TIME AT 7. CON VE RSION REACTION TIME IN HOURS I I NV ENT 0R5 Fsrae lfizwnses Haws flea 679E072 I ATTORNEY-S" United States Patent Ofitice dfit'ilfid d Patented Nov. 7, 1967 3,351,656 METHQD FUR MAKING AN ALKALI METAL SALT F HEPTAGEJUQONIC ACID Peter Leenders, Allendale, NJL, and Hans G. Creutz, De-

troit, Mich, assignors, by mesne assignments, to Allied Research Products, Inc. (formerly Aliied Richardson, Inc), Baltimore, Md, a corporation of Beiaware Original application Oct. 12, 1961, Set. N 144,725, now Patent No. 3,219,560, dated Nov. 23, 15 65. Divided and this application May 18, 1965, Ser. No. 468,665

3 Claims. (Cl. 260-528) This application is a continuation-in-part of our copending application Ser. No. 46,102, filed July 29, 1960, now US. Patent 3,084,112, and a division of copending application Scr. No. 144,725, filed Oct. 12, 1961, now US. Patent 3,219,560.

The present invention relates to electrodepositing copper from an aqueous alkaline cyanide copper plating bath and to improved compositions for such bath The aqueous alkaline cyanide plating bath serves for copper-striking steel, which cannot be plated with an adherent deposit from an acid bath, the initial plating of zinc die castings, for plating an undercoat of copper bebore nickel plating and for plating various other base metals. A typical formulation for such baths comprises copper cyanide, potassium cyanide and sodium hydroxide.

Among the disadvantages of the cyanide bath is included the accumulation of sodium carbonate, a by-product of sodium cyanide decomposition, which results in decreased anode efiiciency. It has been proposed to control such accumulation by, for example, freezing out the carbonate through cooling to 30 F. or by precipitation 4 by adding certain calcium salts. However, the freezing out operation as well as the precipitation methods are cumbersome and expensive.

Metallic impurities in cyanide baths known to be harmful include chromium Cr+ which reduces cathode efii ciency and may result in blistering or peeling of any subsequent plate. The chromium may be reduced with sodium hydrosulphite, but again, sulphur thereby introduced into the bath is highly undesirable.

It is therefore an object of this invention to eliminate the disadvantages normally associated with the use of alkaline cyanide copper plating baths.

Another object of this invention is to eliminate undesirable sodium carbonate accumulation in such baths.

An additional object of this invention is to increase the anode efficiency in such baths.

A further object of this invention is to reduce the hexavalent chromium content of alkaline cyanide copper plating baths.

V It is a still further object of this invention to provide such baths having good chelating and complcxing properties for most two and three valent metals.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereafter, it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

It has now been found that these objects can be attained by incorporating in the alkaline cyanide copper plating bath a sugar heptonic acid. As the sugar heptonic acid there can be employed ot-heptagluconic acid, B-heptagluconic acid, a-mannoheptonic acid, u-galacto-heptonic acid, fl-galacto-heptonic acid, fructoheptonic acid and rhamnoheptonic acid. Both the D and L forms of the sugar acids can be employed. The sugar acids are normally employed as their alkali metal salts, e.g., sodium heptagluconate and potassium heptagluconate. Even if the free sugar acid is employed, it is converted to the alkali metal salt in the cyanide bath.

These sugar heptonic acids and the alkali salts thereof were disclosed in the copending application Ser. No. 46,102, new Patent No. 3,084,112, as additives to eliminate staining and other undesirable effects caused by the incorporation of acetylenic brighteners in aqueous alkaline cyanide copper plating baths. We have now found that the sugar heptonic acids may be eifectively used alone as additives.

The preferred sugar acid materials is a mixture of potassium or D-heptagluconate and potassium [3 D-heptagluconate made by reacting D-glucose with potassium cyanide and hydrolizing the glucose cyanohydrine.

A simplified reaction scheme is as follows:

This material is identified as potassium heptagluconate in Example 2. In place of the potassium salt, sodium heptagluconate can be employed with similar effect.

Example 1 Ingredient Pounds Grams/Liter Dextrose monohydrate 1, 500 399 Potassium cyanide 500 133 Water to make 450 gallons 250 gallons of water was placed in a tank and the dextrose monohydrate added and dissolved. The potassium cyanide was then added together with enough water to bring the total volume to 450 gallons. The ensuing reaction was slightly exothermic and the temperature rose slowly and remained within the range of from to F. The mixture was agitated and after about 90% of the material was converted (determined by titrating the free cyanide remaining and/ or by calculating the amount of unreacted dextrose with Fehlings solution) 25 pounds of potassium cyanide was added to speed up the reaction. When less than 40 grams per liter of unreacted dextrose was left in the product the solution was heated to boiling for about one hour to hydrolize the glucose cyanohydrine and to drive off the ammonia. After cooling to about F. 60 pounds of 35% hydrogen peroxide was added and the mix- 70 ture cooled to room temperature and stored.

gen peroxide used may range between about 50 and 100 pounds of the 35% solution. It is to be understood that sodium heptagluconate may be prepared from dextrose and sodium cyanide and that salts of other sugar heptonic acids may be similarly produced.

As illustrative of the reaction activity in the production of the potassium salt, there is shown in the single figure of the accompanying drawing a curve, the ordinates of which are given in terms of percent conversion of the glucose to glucose cyanohydrine and the abscissae in terms of reaction time in hours. The curve was constructed from values attained in Example 1. The curve was plotted for a reaction time of four hours and slopes sharply at first and then more gradually after a reaction time of about two hours until a 90% conversion value is reached.

Among the outstanding properties of the alkali metal heptagluconates are:

(1) Improved chelating and complexing properties for most two and three valent metals.

(2) Improved effectiveness in anode depolarization.

(3) Brightening effect.

(4) Effective depression of reverse leveling caused by many primary brighteners.

(5) Ability to reduce hexavalent chromium.

(6) Ability to produce smooth grain refined deposits.

The alkali cyanide copper plating bath can be that in standard operation other than for the above additive. Such baths usually contain from to 75 grams per liter of copper and from 45 to 145 grams per liter of an alkali metal cyanide. While the sugar heptonic acid can be employed in an amount of from 1.0 to 100 grams per liter, it is usually employed in an amount of from 10 to 60 grams per liter.

Typical ranges of materials and conditions are:

Copper cyanide grams/liter to 90 Potassium cyanide do.. 45 to 145 Potassium hydroxide do 7.5 to 37.5 pH 12 to 14 Temperature F 100 to 175 Cathode current density amp./sq. ft 1 to 80 Anode current density do 1 to 30 Potassium heptagluconate grams/liter 10 to 60 Potassium carbonate do 0 to- 110 Rochelle salt do 0 to 45 As a result of the present invention smooth copper electrodeposits are obtained from alkaline cyanide copper plating solutions on conventional base metals such as iron, steel, nickel, lead, copper and alloys, e.g., brass. With steel or zinc preferably the base metal is given an initial thin flash of copper from a low efiiciency cyanide copper b ath.

In the specification and claims, all proportions are by weight unless otherwise indicated.

In Examples 2 and 3, the anode and cathode efficiencies of baths containing alkali heptagluconates were determined. The plating operations were carried out in a 450 ml. test cell having brass cathodes at a temperature of 150 F.

Wetting agents can be added such as lauryl oxyethylsulphate, nonylphenol-polyethylene oxide, sodium toluene sulphonate, potassium naphthalene bismethylene sulphonate or certain cationic wetting agents.

In the examples, remarkably good anode eificiencies were obtained over a current density range from 25-40 amperes/sq. ft. The anode efficiencies can further be improved if a combination of heptagluconates with other complexing or chelating agents, such as ethylene diamine tetracetic acid or Rochelle salt is used, with the heptagluconate being the main constituent in this combination.

l ExampleZ Material: Proportions (pounds) Rochelle salt 170 Sodium benzoate 1 EDTA (40%) 40 Dextrose 9 Potassium heptagluconate (of 50% solution) 730 Water to make gallons.

Example 3 Material: Proportions (pounds) Sodium benzoate 1 EDTA (40%) 40 Dextrose 8 Potassium heptag-luconate (of 50% solution) Water to make 115 gallons.

The materials prepared in Examples 2 and 3 were incorporated in amounts of 5% by weight in plating baths containing:

Oz./gal. CuCN 8.0 KCN 1.3 NaOH 1.8

The results of the efliciency tests, all of which were run without agitation, are given in Table I.

The addition of an alkali metal heptagluconate to an aqueous alkaline cyanide copper plating bath increases the anode efiiciency in the solution and gives a smoother copper deposit. This is due to the effect of the heptagluconate of minimizing the roughness-causing films produced by the anodes. In addition, deleterious effects of metallic contaminants capable of interfering with the performance of conventional metallic or organic brighteners are also minimized.

What is claimed is:

l. A method for producing an alkali metal salt of heptagluconic acid which comprises reacting d-glucose with an alkali metal cyanide, hydrolyzing the resulting glucose cyanohydrine, driving 01f the ammonia produced thereby, treating the hydrolyzed and ammonia-free glucose cyanohyd-rine with hydrogen peroxide and recovering said alkali metal salt of heptagluconic acid.

2. The method of claim 1 wherein the d-glucose is reacted with the cyanide at a temperature ranging from 90-130" F.

3. The method of claim 2 wherein the temperature ranges from 115-120" F.

References Cited UNITED STATES PATENTS 2,606,918 8/1952 Isbell 260-528 X 2,735,866 2/1956 Clevenot 260-528 X 3,084,188 4/1963 Horn et a1. 260-528 OTHER REFERENCES Pigman: The Carbohydrates, Academic Press Inc., New York, 1957, page 106.

LORRAINE A. WEINBERGER, Primary Examiner.

I. R. PELLMAN, M. WEBSTER, Assistant Examiners. 

1. A METHOD FOR PRODUCTING AN ALKALI METAL SALT OF HEPTAGLUCONIC ACID WHICH COMPRISES REACTING D-GLUCOSE WITH AN ALKALI METAL CYANIDE, HYDROLYZING THE RESULTING GLUCOSE CYANOHYDRINE, DRIVING OFFTHE AMMONIA PRODUCED THEREBY, TREATING THE HYDROLYZED AND AMMONIA-FREE GLUCOSE CYANOHYDRINE WITH HYDROGEN PEROXIDE AND RECOVERING SAID ALKALI METAL SALT OF HEPTAGLUCONIC ACID. 